Avoid explicit CASA read locking by opening tables in 'usernoread' mode

[sjperkins]

• Tests added / passed

  $ py.test -v -s daskms/tests

  If the pep8 tests fail, the quickest way to correct
  this is to run autopep8 and then flake8 and
  pycodestyle to fix the remaining issues.

  $ pip install -U autopep8 flake8 pycodestyle
  $ autopep8 -r -i daskms
  $ flake8 daskms
  $ pycodestyle daskms
  

• Fully documented, including HISTORY.rst for all changes
  and one of the docs/*-api.rst files for new API

  To build the docs locally:

  pip install -r requirements.readthedocs.txt
  cd docs
  READTHEDOCS=True make html
  

[sjperkins]

The test cases seem happy with this @JSKenyon. Want to give it a whirl?

[JSKenyon]

I gave this a whirl but I cannot see an obvious improvement:

The reads still seem to be locking up. Is it plausible that the tables are still being locked?

[sjperkins]

@JSKenyon I've disabled locking on the TAQL queries